Resistance thermometer bulb



March- 4, 1952 K. J. KNuDsEN 2,588,014 RESISTANCE THERMOMETER BULB Filed April 27, 1949 :inventor (Ittornegl Patented Mar. 4, 1952 RESISTANCE THERMOMETER BULB Knud J1 Knudsen,.Naugatuck, Conn., assignor to The Lewis Engineering Company, Naugatuck, Conn., a corporation 'of Connecticut Application April `27, 1949,v Serial No.` 90,009

11 Claims.

This invention relates to're'sistancefthermometer bulbs.

An object of the inventionis ato-provide Aan-improved resistance thermometer bulb which isextremely sensitiveand rapid inv its,- response to4 temperature changes.

Another objectA ofthe inventionristo provide an improved resistance bulb-of this` type, which is very accurate and reliablein-operationover a-n extended period of use.

Yet another object-foi'4 the invention is to `provide an improved resistance bulb-characterized as above, which-has relativelyy fewfparts and is of simple and economical-construction.`

A still further object4 of the invention isfto provide a resistance thermometer bulb 1in accordance With theforegoing, Whichis sturdy in construction and resistanttoshock andevibration.

In accomplishing theaboveV` objects I provide, in accordance with theinvention, a-tubular metal casing adapted to beinser-ted into a well inY a heated instrumentality suchv as an-engine block or the like. Within the casing-there is provided a coil of heat-responsivawire, all/convolutions of which are closely` adjacentrthe inner casing walls. convolutions andthel inside ofv the casi-ng extremely small and of aminute order, thereby tofpromote anextremely eiiicient andefiective transfer of heat fromV thecasing tojthe coil.

I further provide means, one formeof which comprises a one-piece tubulary coil form f of very thin metaland small mass; as disclosed in the embodiment of the invention. illustrated! herein, for securely supporting the coil in the casing in said closely= spaced-relationship'tothe Walls, and at the same timeaiding ratherl than hindering the conformance of the coil temperature with thatof the casing. y

To electrically insulate thecoi-lfrom-the casing aV tough, heat resistant insulating means is -provided,v which may be.anextremelythinlm of silicone coatedon the.wire. Ishavefoundlthat suchsilicone coating provides an advantageous and adequate electric insulation between the spaced coil convolutionsandv the casing, which will readily withstand the relatively high temperatures to which resistance bulbsare subjected, and which is stablei tough and resistant to abrasion. Byy locating. the coiln convolution in such close proximity tothe insiderwalls ofthe-.casing an extremely sensitive, .rapid lresponse device results, which quickly.`v changes resistance?- with changes in.k temperature yof 'the' .heated `instrumen` tality in which thecasing ismountedi I make the distance betweeny saidVv said In conjunction with this sensitive response assembly, connector junctions are provided having opposed E. M. F.s, said junctions being located closely adjacent each other whereby they are subjected to equal heat, and therefore generate equal voltages which canceleachfother out. This organization results in an accurate and reliably performing resistancebulb.

The mounting for the heat-responsive coil, which comprises a single tubular member, carries extension strips which support the junctions or terminals for the coil whereby very few-parts are required. The structure is therefore simple and economical to fabricate and produce.

Other features and advantages will hereinafter appear.

In the accompanying drawing:

Figure l is an axial sectional view of the improved resistance thermometer bulb of this invention.

Fig. 2 is an enlarged detail in section, showing the mounting for thevconnections or junctures of the coils.-

Fig. 3 is anend elevational View of therheatresponsive coil and coil form assembly.

Fig. 4 is an end view of thecoil form carried by an arbor and reduced slightly in diameter prior to the Winding of the heat-responsive coil, and

Fig. 5 is a transverse sectional view taken on line 5--5 of Figs. 1 and 2.

As shown, the present improved resistance bulb comprises an elongate tubular metal casing IIJ having a straight or cylindrical portion II, a conical or ared portion I2 and a mouth portion I3, the latter carrying a sealing cap I 4 insulat ingly mounting connecting pins I5.

The casing I0 is adapted to be carried by a suitable tting and mounted to extend into a well of a heated instrumentality such as an engine block or' the like, as is well understood in the art.

The small end of the casing I 0 is provided with ardisk-like closure member I6 which is secured in place in any suitable manner, as by silver solder I1.

The casing I0, cap I4 and closure disk I 6 may be advantageously made of stainless steel.

In accordance With the invention,` a heatresponsive coil I8 is provided within the casing I0 to lie closely adjacent the inner casing walls. the distance between the coil convolution's and the' insideV of vthe casing portion II being'extremely small croi a' minute order so as to promote an extremely. effective and efficient transfer of heat from the casing to the coil. Preferably the coil I8 is of nickel wire, although other suitable metal may be used.

The coil I8 is, in the specic embodiment of the invention illustrated herein, a single layer coil having convolutions |8a uniformly spaced apart a slight amount, as for example a thirtysecond of an inch.

For the purpose of securely supporting the coil I8 in its position closely adjacent the inside walls of the casing portion and to enhance the response of the coil to changes in the temperature of the casing, I provide by the present invention a novel tubular coil form I9 of very thin metal and small mass, the form being longitudinally split to provide a longitudinal slot 2l] and the adjacent edges of the coil form on opposite sides of the slot being turned in to provide flanges 2| (Fig. 3) and rounded portions or surfaces 22.

The heat-responsive wire of the coil I8 is insulated with a silicone coating, preferably prior to the wire being wound on the coil form I9. In order to maintain the convolutions of the coil I8 taut, prior to winding the coil, I mount the coil form |9 on a tubular mandrel or arbor 23 which is also longitudinally split whereby the longitudinal edges 23a of the mandrel engage the inturned flanges 2| of the coil form and pull the latter in to a slightly smaller diameter. The coil form |9is preferably made of the same metal (nickel) as the coil I8, and is resilient and extremely thin, on the order of .002 inch thick, whereby it has a very small mass. In consequence of this, the tendency of the coil form I9 is to aid the conformance of the coil temperature with thatof the casing. This is because by virtue of its small mass and large area v'exposed to the inside walls of the casing, the temperature of the coil form itself will Yvery closely follow the temperature of the casing. Heat radiated from the casing interior will be effectively intercepted by the coil form, as can be readily understood, and this heat will be quickly transferred to the convolutions |8a of the coil I8.

When the coil form I9 is mounted on the arbor 23, the latter may be placed in a lathe or coil winding machine and the coil I8 wound on the form. To protect the winding I8, the end portions thereof may have threads 24 of glass fibers interposed between the coil convolutions, and the entire coil and coil form may be bonded together by the application of a suitable silicone adhesive during the winding operation. One end 25 of the coil I8 may be brazed, welded, or otherwise suitably secured to the coil form I9 as shown in Fig. l, whereby the form functions as a ground return for the coil. a

4 cylindrical portion of the casing, the dimensions of which are such that va close fit is provided. The convolutions of the coil I8 are preferably at all points practically in contact with the inner surface of said casing portion.

If tightness is encountered during the insertion of the coil I8 and coil form I9 into the casing I0, the coil and form may yield and become smaller in diameter, enabling the inserting operation to readily proceed. This yield is made possible by the bent portions of the coil convolutions, which span the slot 29 and extend slightly into the same. I have found that the coil and casing may be so dimensioned that the casing slightly compresses the coil and coil form, causing a continual slight pressure to exist whereby the heat exchange is facilitated further.

The double silicone coating on the wire coil (one prior to winding and one subsequent to winding of the coil) effectively insulates the coil convolutions from`the casing ID, while at the same time enabling efficient transfer of heat to take place from the casing tothe coil. Preferably, as shown in Fig. l, an insulating disk 28 of woven glass bers, impregnated with silicone; is disposed adjacent the end closure I8 of the casing to prevent contact between the closure and the coil form I9 which constitutes part of the electrical circuit of the bulb. a

For the purpose of carrying Calibrating means for the coil I8 and providing for electrical connections thereto, terminal members 21 in the form of nickel strips having reverse bends in them are welded to the inside of the coil form prior to the winding of the coil. The strips have Iuxtaposed semicylindrical cooperable portions .8 adapted to receive a lead wire 29 whereby electrical connection may be effected to the coil form I9. Preferably the wire 29 and strip portions 2 8 are all welded or bonded together in a single operation. It will be noted that the strips 21, especially the portions 28 thereof, constitute in effect a stud which extends axially from the end of the coil form I9.

In order to insulatedly carry a Calibrating coil for the heat-responsive coil I8, an insulating sleeve 38, preferably formed of woven glass fibers impregnated with silicone, is slipped over the lead wire 29 and the portions 28 of the connector strips 21. Adjacent the strip portions 28 and encircling the sleeve 38 a metal band 3| is provided, and a second metal band 32 is mounted on the sleeve 30 adjacent its other end. Between the bands 3| and 32 a Calibrating coil 33 is wound, having its ends respectively joined to the bands 3| and 32. The other end of the heat-responsive Y coil I8 is also joined to the band 3 I, 'and a second As shown in Figs. 3 and 5, the portions of the coil convolutions which bridge the slot 2|!V are bent inward, into the slot a slight distance, after the winding of the coil has been completed and while it is still on the mandrel. By doing this, ,variation in the coil diameter is made possible, for a purpose which is explained below.

, I have found that a coil and coil form assembly as constructed above provides Va highly advantageous heat-responsive unit in conjunction with the casing I9. When the coil and coil form are removed from the mandrel 23, the form I9 tends to expand diametrically and to maintain the convvolutions of the coil I8 taut. The assemblage is closely controlled as to its effective outside diameter by the mandrel 23, and after removal from the mandrel it may be readily"slipped' into the lead wire 34 is joined to the band 32.

The lead wires 29 and 34 and the calibrating coil 33 are preferably of low-temperature coefficient metal such as that known commercially as constantan, and the bands 3| and 32 are preferably of stainless steel. While the coil I8, coil form I9 andconnector strips 21 are preferably made of nickel, it should be understood that other suitable metals having high-temperature coefficients of resistance may be used, the essential consideration being that all said components are of the same material.

The reason for this is as follows: The metal band 3| 'is inthehsame location as the portions 28 of the connecting strips 21, and is closely adjacentl the said portions. vConsequently the band and the connector portions will always remain at substantially the "same'temperatures, This,

together-with thefmaking'foffthelcoil, coil form and-'1 strips fof the! same?. metal; isV responsible in party for the 'important' featureof the present invention whereby accurate responses" are obtained throughout the range of" temperature of the bulb. The F. o1H thermocouple effect produced .by the juncture between therbandi 3l and the? end of the Calibrating coil33 can be combinedwith thatbetween the band'an'd' the heat-responsive coil I8.' and-'considered asa single E.-M.` F. produced in the present'case, between constantanandnickel. This E. M.' F. will thus be equal to the E. M. between the constantan leadwire 29 and the nickel connecting. strip portions 281dueto their both beingclose to each otherv and' thereforegalways. at the same'v ternperature. These E. M; F.swill.therefore yoppose and cancelA out each other whereby inaccuracy inthe' response of the resistanceV bulbv will be greatly reduced.

The improvedl resistance bulb as aboveA constructed is extremely simple, being constituted of' relatively few parts which are f of economical construction and assembly. The structure has been found to be sturdy and resistant to shock and vibration, thus making for reliability in operation over an extended period of use.

By virtue of the close proximity between the inner walls of the casing l Il and the convolutions 18d ofthe heat-responsive coil, efficient exchange of lheat is effected whereby the response of the resistance bulb rto temperature changes is rapid and accurate.

The silicone insulating films between the coil I8 and the coil form IS and casing I are effective in resisting rupture and providing adequate heat resistance and electricalinsulation. I have found that the pressure maintained on the coil convolutions by the compressed coil form I9 is relatively light, and much less than that required to cause a rupture of the insulating lm.

Variations and modifications may bev made within thev scope of this invention and portions of the improvementsmay be used without others.

I claim:

l. A rapid-response resistance thermometer bulb comprising a tubular metal casing adapted to be inserted into a well in a heated instrumentality; a coil of heat-responsive wire disposed within the casing adjacent the inner walls thereof, the distance between the coil convolutions and the inside of the casing being of a minute order to promote an efficient transfer of heat; means, including a longitudinally-split metal tube on which the coil is wound, for supporting the coil in the casing in said closely-spaced relationship to the inner casing walls, said tube being biased to maintain the coil convolutions taut; and heatresistant means for electrically insulating the coil from the casing.

2. A rapid-response resistance ,thermometer bulb comprising a tubular metal adapted to be inserted into a well in a heated instrumentality; a coil of heat-responsive wire disposed within the casing adjacent the inner Walls thereof, the distance between the coil convolutions and the inside of the casing being of a minute order to promote an eiiicient transfer of heat; means for internally supporting the coil in the casing in said closely-spaced relationship to the inner casing walls, said means including a resilient metal coil form constructed and biased to maintain a uniform, relatively light pressure on the insides of the coil convolutions; and a thin, heat-resistant lm of relatively tough insulating material disposed!- between the'coil convolutionsand coil form, said iilm"normallyrequiring pressuresito rupture it whichare greatly in excess of the pressure existing betweenv the coil form and coil convolutions. A

3. A. rapid-response resistance thermometer bulb comprising a tubular metal casing adapted to be inserted into a well in a heated instrumentality; a coil of'heat-responsive wire wound in a simplehelix having a straight axis, said coil being disposed within the casing adjacent the inner walls thereof with itsl axis extending longitudinally ofthe casing, the distancev between all portions of the wire in the coil convolutions and the inside of the casing being of a minute order to promote. an efficient transfer of heat, and the coil convolutions being spaced from each other; means for internally supporting the coil in the casing in said closely-spaced relationship to the inner casing walls, including a smooth cylindrical tubular metal memberV on which the coil is wound, said member being-in intimate heat-conducting relation with said coil, and being adapted to intercept heat radiated inwardly from said casing and heat-resistant means for electrically insulating the coil from the casing.

4. A rapid-response resistance thermometer bulb comprising a tubular metal casing adapted to be inserted into a well in a heated instrumentality; a heat-absorbent and heat-conducting coil form having a smooth cylindrical outer surface disposed within and spaced from said casing; heat-responsive means comprising solely a single-layer coil of heat-responsive wire wound in a simple helix having a straight axis, said coil being carried'by the coil form with its axis extending longitudinally of the form and occupying space between the form and the casing, the coil convolution being spaced to enable heat from the casing to be radiated to the coil form and the distance between all portions ofthe wire in the coil convolutions and the inner surface of the casing being of a minute order to promote an eicient transfer of heat; and a thin film of heat-resistant electrically-insulating material'located between the coil and said innerV casing surface, all of said coil convolutions beingin good heat-conducting relation to both the casing-'and the coil form.

5. A rapid-response resistance thermometer bulb comprising relatively thin, tube-shaped, outer and inner metal members having closely spaced walls providing for relatively high degree of heat exchange, the inner member having a smooth cylindrical surface; heat-response means comprising solely a single-layer coil of heatresponsive wire wound in a simple helix having a straight axis, said coil being carried by the inner member with its axis extending longitudinally of the member, and occupying space between the members; and thin films of heat-resistant electrically-insulating material located between the coil and the adjacent surfaces of said members, the coil convolutions being spaced from each other and the distance between all portions of the wire in the coil convolutions and the adjacent surfaces of the outer and inner members being of a minute order whereby heat is efficiently transferred from the members to each other and to the coil.

6. A resistance thermometer bulb comprising an elongate tubular sheath; a coil form of heatresponsive, low temperature coefficient metal, disposed in said sheath; a pair of connector members within the sheath,Y one constituted of the same metal as the coil form; means electrically connecting together the coil form and said one connector member; a pair of low temperature coefficient wires of the same metal, disposed in said sheath and respectively joined to said connector members; and a coil of heatresponsive wire made of the same metal as the coil form, wound on said form and having one end connected thereto and the other end connected to the other connector member, the three junctures between the said wires and connector members being disposed substantially at the same point measured longitudinally of the sheath whereby their temperatures are substantially equal, and their E.M.F.s cancel each other.

7. The invention as defined in claim 1 in which the coil form has a longitudinal slot and is compressible to a smaller diameter, and in which portions of the coil convolutions spanning the slot are bent inward from the helix defined by said convolutions, the coil and coil form being compressed diametrically, when in the casing, by engagement with the casing walls.

8. A resistance thermometer bulb comprising a metal coil form; a metal connector stud projecting from one end of the coil form and electrically connected thereto; a` low temperature coeicient lead wire electrically joined to said stud and extending axially therefrom; an insulating sleeve encircling said stud and lead wire and the juncture thereof; a calibrating coil wound on said sleeve; a connector member secured around said sleeve at said juncture; a heatresponsive coil wound on said coil form, one end of each of said coils being connected to said connector member and the other end of the heatresponsive coil being connected to said coil form; and a second 10W temperature coefcient wire connected to the other end of the Calibrating coil.

9. A heat-responsive subassembly for a resistance vthermometer bulb, comprising a resilient, longitudinally split, elongate tubular metal coil form; a coil of heat-responsive wire wound on said coil form, the latter being compressed diametrically by the coil whereby the coil convolutions are held taut; and heat-resistant, electrical insulating means bonding said coil to the coil form.

10. A heat-responsive subassembly for aresistance thermometer bulb, comprising a resilient, longitudinally split, elongate tubular metal coil form having inturned longitudinally extending flanges along the split portions; a coil of heatresponsive wire wound on said coil form, the latter being compressed diametrically by the coil whereby the coil convolutions are held taut; and heat-resistant, electrical insulating means bonding said coil to the coil form.

11. A rapid-response resistance thermometer bulb comprising a tubular metal casing adapted to be inserted into a well in a heated instrumentality; heat-responsive means comprising solely a single-layer coil of heat-responsive wire Wound in a simple helix having a straight axis, said coil being disposed within the casing adjacent the inner walls thereof with the coil axis extending longitudinally of the casing,'the coil convolutions being spaced apart and the distance between all portions of the wire in the coil convolutions and the inside of the casing being of a minute order to promote an eicient transfer of heat; means for internally supporting the coil in the casing in said closely-spaced relationship to the inner casing walls, including a thin metal tube-like member of relatively large area and small mass and having a smooth surface, disposed in intimate heat-conducting relation with said coil and adapted to intercept inwardly from said casing; and heat-resistant means for electrically insulating the coil from the casing.

KNUD J. KNUDSEN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,411,396 Wilson et al Apr. 4, 1922 2,156,826 Ullman May 2, 1939 2,372,840 Mattern Apr. 3, 1945 2,379,530 Lederer July 3, 1945 2,476,099 Knudsen July 12, 1949 

